1. Field of the Invention
This invention relates to treating a subterranean reservoir penetrated by at least one well wherein the relative water/petroleum movement through the reservoir is reduced. More particularly, the invention relates to such a treatment wherein the flow of water through the water-producing zones of the reservoir is reduced while the flow of petroleum through the petrolume-producing zones remains substantially unchanged.
2. Description of the Prior Art
In producing petroleum from subterranean reservoirs penetrated by one or more wells, it is often desired, at some point in the productive life of the reservoir, to inject one or more treating fluids via one or more of the wells and subsequently produce the same well or wells. In such operations, it is often desired that reservoir petroleum be easily produced through the last-injected treating fluid but that the flow of a reservoir brine or a previously injected aqueous first treating fluid therethrough be restricted. Examples of such operations include treating the reservoir to reduce the water/oil ratio produced therefrom, treating a reservoir with a scale inhibitor, and the like.
It is known to inject into a reservoir various treating solutions containing a wide variety of either a water-soluble thickening agent or an oil-soluble thickening agent.
U.S. Pat. No. 3,336,977 to Amott describes a method for reducing the water-oil ratio of a production well wherein there is injected prior to the floodwater a suspension of a water-soluble viscosifier modifier in a non-solvent carrier liquid (crude oil). Examples of a viscosity modifier include water-soluble polymers such as modified starch, carboxymethylcellulose, polyacrylamide, partially hydrolyzed polyacrylamide and ethylene oxide polymers.
U.S. Pat. No. 3,483,925 to Slyker covers a squeeze treatment wherein there is sequentially injected into a formation a solution of a scale-inhibiting composition, an aqueous solution of a viscosity-increasing polymer such as polyacrylamide, and a further slug of the solution of a scale-inhibiting composition.
U.S. Pat. No. 3,721,295 to Bott discloses a process for reducing the water/oil ratio at a producing well involving injection into the well of a water-in-oil emulsion containing a dispersion of a finely divided water-soluble vinyl addition polymer (polyacrylamide). The emulsion concentrate can be diluted with an organic liquid such as crude oil. When the emulsion contacts formation water, it inverts releasing the polymer into solution. The resulting increased viscosity solution plugs channels in the formation.
U.S. Pat. No. 3,724,551 to Troscinski et al. is similar to the above patent except that the injection of emulsion-containing dispersed polymer is preceeded by injection of a slug of brine containing a water-soluble surfactant.
U.S. Pat. No. 3,330,345 to Henderson et al. involves a miscible drive process wherein there is injected into a formation: (1) a buffer slug of a hydrocarbon liquid containing a thickening agent, for example, polymethyl laurylate, polyalkyl styrene, polybutadiene and soaps of certain monocarboxylic acids; (2) an amphiphatic solvent such as a monohydroxy alcohol having from one to four carbon atoms per molecule; and (3) a scavenging fluid such as chemically treated water.
While the techniques disclosed in the above patents have certain advantages, need remains for further improvement in the control of water/petroleum ratios of producing wells and in prolonging the life of scale inhibitors injected into wells. It has not been previously known to carry out a well treatment wherein there is injected into a reservoir a treating agent containing both a water-soluble thickening agent and an oil-soluble thickening agent.
Accordingly, it is a principal object of this invention to provide a method for restricting the flow of an aqueous fluid through a reservoir.
It is another object of the invention to provide such a method wherein the water/petroleum ratio produced from a well is reduced.
It is still another object of the invention to provide such a method wherein the amount of water produced from a well is reduced without a substantial reduction in the amount of oil produced therefrom.
It is a further object of the invention to provide such a method wherein the life of a scale inhibitor injected into a reservoir is prolonged.
Other objects, advantages and features of the invention will be apparent from the following description.